The goal of this proposal is to study how auditory information is integrated with visual information to generate purposeful orienting responses. We propose to study this sensorimotor integration in the superior colliculus (SC) using physiological recordings in behaving cats trained to saccade to visual and acoustic targets, and light and electron microscopic neuroanatomical techniques. The PI of this project is a New Investigator. An essential premise of this proposal is that important elements of the current model of sensorimotor integration in the SC of the cat are based on data from anesthetized cats, and anesthetics profoundly affect the physiology of SC neurons. One of the building blocks of this model, the enhancement of SC responses to bimodal (visual + auditory) stimuli, is thought to be a mechanism to increase the likelihood of behavioral responses to relevant stimuli. Our preliminary findings in the behaving cat do not reveal enhancement of SC units under experimental conditions similar to those used in studies of the anesthetized preparation. Accordingly, in Specific Aim number 1 we propose to complete our studies of SC single unit responses to unimodal and bimodal (auditory, visual) stimuli in the standard-trained cat. We will test our hypothesis that enhancement results from spurious effects of anesthetics in Specific Aim number 2 by recording from the same SC units under both behaving and anesthetized conditions. Our hypothesis that sodium pentobarbital affects inhibitory inputs to the SC will be tested in Specific Aim number 3, where we will chemically deactivate the major source of inhibitory input to the SC, the substantia nigra pars reticulata (Snr). Specific Aim number 4 will determine if the behavioral relevance of sensory stimuli can lead to enhancement of the SC of the specially-trained behaving cat, while Specific Aim numbers 5, 6, and 7 are designed to explore the inputs to the SC that might underlie sensorimotor integration of auditory-related information.